Justin Bieber had a hair-raising moment when he was trapped in an elevator for 20 minutes backstage at a concert in London on Saturday.

The Baby hitmaker was on the bill for the Capital FM Summertime Ball, but he was thrown into a panic when an elevator he was travelling in with several fans jammed.

A source tells Britain's The Sun newspaper, "The girls couldn't believe their luck to be stuck there with him. They were sweating and nearly fainting with Biebermania before they got out."

But the mishap failed to prevent Bieber from wowing the crowd when he finally took to the stage at Wembley Stadium, where he performed a hits-packed set and even called fellow Canadian singer Carly Rae Jepsen onstage to duet on her hit Call Me Maybe.

After his performance, Bieber paid tribute to his fans, telling radio station Capital FM, "It's crazy, I mean, just to have the fan base. You know, going out there and seeing 80,000 people, and half of those people have my sign up! It's crazy!"